Replace eval with eval_code_async to support top level await

[whitphx]

In the Pyodide environment, there are some restrictions for example time.sleep() cannot be used. Using async methods such as asyncio.sleep() would be the workaround, but in Streamlit app scripts it's not possible because Streamlit executes the script with eval() so the top-level await-s cannot be used.

So try to replace the native eval() with pyodide.code.eval_code_async: https://pyodide.org/en/stable/usage/api/python-api/code.html#pyodide.code.eval_code_async to support the top-level await-s in the user scripts.

[stefanonardo]

Hi @whitphx , is there any update on this?

[whitphx]

Hmm, it's not straightforward.

It's not eval() but exec() that is used in Streamlit.
https://github.com/streamlit/streamlit/blob/1.19.0/lib/streamlit/runtime/scriptrunner/script_runner.py#L565
It seems not to be simply replaced with Pyodide's async exec?

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Possible options:

• Manipulate the code fed to exec() to be async by wrapping the original code with async def some_func(): and asyncio.run().

[whitphx]

The solution would be whitphx/streamlit@d116796

• compile the source code with ast.PyCF_ALLOW_TOP_LEVEL_AWAIT, which outputs the code object as a coroutine when the source includes top-level await-s.
• Run the compiled code object with eval() instead of exec() when the code object is a coroutine so that the eval-ed coroutine is awaited. To await the eval-ed coroutine, its wrapper method, ScriptRunner._run_script(), needed to be modified to be an async function.